Bio-inspired Maillard-Like reactions enable a simple and sensitive assay for colorimetric detection of methylglyoxal

Visual Detection of Methylglyoxal in Multiple Scenarios via NIR-Excitable Reversible Ratiometric Fluorescent Hydrogel Sensor

Methylglyoxal is considered a key indicator in evaluating wine flavor and quality, as well as an important marker for diabetic pathological syndromes. Rapid and accurate quantitative detection of methylglyoxal is essential in scenarios of wine production standards and human health monitoring. Herein, we report a visual method for detecting methylglyoxal via an NIR-excitable reversible ratiometric fluorescent hydrogel sensor, where NIR-excited upconversion nanoparticles serve as energy donors and eosin B acts as the energy acceptor, together forming an integrated ratiometric nanophotonic probe that ensures the accuracy of detection without being affected by various background fluorescence interference in different scenarios. The integrated optical probe is combined with a 3D network hydrogel to design a sensing patch that can be easily regenerated through simple treatment, exhibiting a distinct optical color response. Upon the addition of methylglyoxal, the G/R value of the sensing patch changes, enabling the real-time quantitative detection of methylglyoxal. Additionally, we combined the hydrogel sensing patch with a smartphone to create a portable sensing platform for the convenient visual detection of methylglyoxal. The probe and hydrogel sensing patch have detection limits for methylglyoxal as low as 59 and 75.4 nM, respectively. The portable sensing patch designed here provides an effective strategy for standardizing the wine production process and monitoring patient health.

Application of Intelligent Response Fluorescent Probe in Breast Cancer

As one of the leading cancers threatening women's lives and health, breast cancer is challenging to treat and often irreversible in advanced cases, highlighting the critical importance of early detection and intervention. In recent years, fluorescent probe technology, a revolutionary in vivo imaging tool, has gained attention in medical research for its ability to improve tumor visualization significantly. This review focuses on recent advances in intelligent, responsive fluorescent probes, particularly in the field of breast cancer, which are divided into five categories, near-infrared responsive, fluorescein-labeled, pH-responsive, redox-dependent, and enzyme-triggered fluorescent probes, each of which has a different value for application based on its unique biological response mechanism. In addition, this review also covers the strategy of combining fluorescent probes with various anti-tumor drugs, aiming to reveal the possibility of synergistic effects between the two in breast cancer treatment and provide a solid theoretical platform for the clinical translation of fluorescent probe technology, which is expected to promote the expansion of cancer treatment technology.

Photo-Enhanced Chemo-Transistor Platform for Ultrasensitive Assay of Small Molecules

Compared with traditional assay techniques, field-effect transistors (FETs) have advantages such as fast response, high sensitivity, being label-free, and point-of-care detection, while lacking generality to detect a wide range of small molecules since most of them are electrically neutral with a weak doping effect. Here, we demonstrate a photo-enhanced chemo-transistor platform based on a synergistic photo-chemical gating effect in order to overcome the aforementioned limitation. Under light irradiation, accumulated photoelectrons generated from covalent organic frameworks offer a photo-gating modulation, amplifying the response to small molecule adsorption including methylglyoxal, p-nitroaniline, nitrobenzene, aniline, and glyoxal when measuring the photocurrent. We perform testing in buffer, artificial urine, sweat, saliva, and diabetic mouse serum. The limit of detection is down to 10^-19 M methylglyoxal, about 5 orders of magnitude lower than existing assay technologies. This work develops a photo-enhanced FET platform to detect small molecules or other neutral species with enhanced sensitivity for applications in fields such as biochemical research, health monitoring, and disease diagnosis.

Design of an activatable NIR-II nanoprobe for the in vivo elucidation of Alzheimer's disease-related variations in methylglyoxal concentrations

Clear elucidation of the changes in Alzheimer's disease (AD)-related methylglyoxal (MGO) levels in vivo is significant yet highly challenging. Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) has gained increasing attention as an observation method in living organisms, but an MGO-activatable fluorescent probe that emits in this region for in vivo brain imaging is lacking because of the existence of the blood-brain barrier (BBB). Herein, a biocompatible Fe3O4 nanoparticle (IONP)-conjugated MGO-activatable NIR-II fluorescent probe (MAM) modified with the peptide T7 (HAIYPRH) (named TM-IONP) is reported for the in situ detection of MGO in a transgenic AD mouse model. In this system, the T7 peptide enhances BBB crossing and brain accumulation by specifically targeting transferrin receptors on the BBB. Due to the MAM probe, TM-IONPs emit fluorescence in the NIR-II region and display high selectivity with an MGO detection limit of 72 nM and a 10-fold increase in the fluorescence signal. After intravenous administration, the TM-IONPs are easily delivered to the brain and pass through the BBB without intervention, and as a result, the brains of AD mice can be noninvasively imaged for the first time by the in situ detection of MGO with a 24.2-fold enhancement in NIR-II fluorescence intensity compared with wild-type mice. Thus, this MGO-activated NIR-II-emitting nanoprobe is potentially useful for early AD diagnosis in clinic.

Rapid sensing and imaging of methylglyoxal in living cells enabled by a near-infrared fluorescent probe

A novel near-infrared fluorescent probe (SWJT-2) has been designed and synthesized for the detection of methylglyoxal (MGO). It showed a low detection limit (0.32 μM), high selectivity and the fastest detection (15 min) over various reactive carbonyl compounds in aqueous solution. SWJT-2 had been successfully applied to bioimaging in HeLa cells to detect exogenous and endogenous MGO.

Mitochondria-targeted fluorescent probe for visualization of exogenous and endogenous methylglyoxal in living cells

An activatable mitochondria-targeted fluorescent probe Hcy-OPD was synthesized for the detection of methylglyoxal (MGO). For the introduction of a preorganized isopropylamino group on the aromatic o-diamine framework to regulate the hindrance effect, Hcy-OPD showed high selectivity and sensitivity (0.22 μM) for monitoring MGO. The probe can be applied successfully in the imaging of exogenous and endogenous MGO in living cells.

A Ratiometric Fluorescence Probe for Selective Detection of ex vivo Methylglyoxal in Diabetic Mice

Accurate monitoring of methylglyoxal (MGO) at cell and living level was crucial to reveal its role in the pathogenesis of diabetes since MGO was closely related to diabetes. Herein, a ratiometric fluorescence strategy was constructed based on the capture probe 2,3-diaminonaphthalene (DAN) for the specific detection of MGO. Compared to the fluorescent probes with a single emission wavelength, the ratiometric mode by monitoring two emissions can effectively avoid the interference from the biological background, and provided additional self-calibration ability, which can realize accurate detection of MGO. The proposed method showed a good linear relationship in the range of 0-75 μm for MGO detection, and the limit of detection was 0.33 μm. DAN responded to MGO with good specificity and was successfully applied for detecting the ex vivo MGO level in plasma of KK-Ay mice as a type II diabetes model. Besides, the prepared DAN test strip can be visualized for rapid semi-quantitative analysis of MGO using the naked eye. Furthermore, human skin fibroblasts and HeLa cells were utilized for exogenous MGO imaging, and ex vivo MGO imaging was performed on tissues of KK-Ay mice. All results indicated that the DAN-based ratiometric fluorescence probe can be used as a potential method to detect the level of MGO, thus enabling indications for the occurrence of diabetes and its complications.

NIR-I fluorescence imaging tumorous methylglyoxal by an activatable nanoprobe based on peptide nanotubes by FRET process

Methylglyoxal (MGO), a glycolysis metabolite with high reactivity, can nonenzymatically modify proteins, lipids and nucleic acids etc., and it is closely related to the development of tumors. The accurate detection and high-performance optical imaging of MGO from deep tumor issues is of great significance for understanding their roles in tumor initiation and progression. Herein, we have presented a nanoprobe D/I-PNTs with emission in the first near infrared (NIR-I) region by employing a fluorescence resonance energy transfer (FRET) process between a far-red emission MGO probe and IR783 based on peptide nanotubes. The nanoplatform extended the emission range of MGO probe through FRET process and avoided complex molecular design and synthesis. The biocompatible peptide nanotubes improved the water solubility of MGO probe. D/I-PNTs was sensitive to MGO with a detection limit of 272 nM and enabled high-resolution NIR-I fluorescence imaging of MGO induced by glyoxalase I (GLO1) inhibitor in tumor with higher penetration depth (∼4 mm) than that in visible (Vis) region (∼3 mm). Most importantly, the FRET process based on the structure characteristics of peptide nanotubes can be a universal approach to realize the extension of emission wavelength and ratio detection of target analytes, which will be a promising strategy for bioimaging in deep tissue with high contrast.

Carbon-nitrogen conjugate-composited Cu1.8S with enhanced peroxidase-like activity for the colorimetric detection of hydrogen peroxide and glutathione

In this work, cystine-glucose Maillard conjugates were composited with Cu_1.8S microspheres (Cu_1.8S-cgmc) to achieve higher sensitivity for the colorimetric analysis. Enhanced peroxidase-like activity was obtained in Cu_1.8S-cgmc with a carbon elemental ratio of 1.83% compared to bare Cu_1.8S. The catalytic activity of Cu_1.8S-cgmc followed Michaelis-Menten kinetic behavior. The Michaelis-Menten constants of Cu_1.8S-cgmc on the substrate was over 2-fold lower than that of the bare Cu_1.8S, indicating the higher affinity of Cu_1.8S-cgmc. The adsorption equilibrium constant of Cu_1.8S-cgmc on the substrate was 9.89-fold higher than that of bare Cu_1.8S based on thermodynamic investigations. The conjugated structure and carboxyl, hydroxyl and amino groups on Cu_1.8S-cgmc improved its hydrophilicity and adsorption on the substrate. The affinity-improved Cu_1.8S-cgmc was applied as a peroxidase mimic in colorimetric detection with promoted sensitivity. Compared to bare Cu_1.8S, Cu_1.8S-cgmc had a 25.5-fold and 19.8-fold lower LOD for H₂O₂ and glutathione, respectively. The Cu_1.8S-cgmc-based colorimetric method showed excellent sensitivity and accuracy in practical colorimetric detection.

An activatable near-infrared fluorescent probe for methylglyoxal imaging in Alzheimer's disease mice

Visual detection of the methylglyoxal (MGO) level in the brain is critical for understanding its role in the onset and progression of AD. Herein, we disclosed a NIR fluorescent probe, DBTPP, for detecting MGO by utilizing a thiadiazole-fused o-phenylenediamine moiety as a MGO-specific sensing unit. DBTPP exhibits a series of distinct advantages, such as NIR emission, high selectivity and sensitivity, excellent acid-stability, and a huge off-on ratio. The probe could accurately monitor both exogenous and endogenous MGO variations in SH-SY5Y cells. Besides, it was able to image the endogenous MGO in a transgenic AD mouse model successfully, suggesting the great potential of MGO as a biomarker for early AD diagnosis.

Cu2+-Modified Boron Nitride Nanosheets-Supported Subnanometer Gold Nanoparticles: An Oxidase-Mimicking Nanoenzyme with Unexpected Oxidation Properties

In recent years, inorganic biomimetic nanozymes that mimic the activity of natural biological enzymes have attracted extensive research interest, and some mimic enzymes have been successfully applied in the fields of biosensing, catalysis, and oncotherapy. Herein, we report the preparation and mechanism study of a novel nanocomposite, Cu²⁺-modified hexagonal boron nitride nanosheets-supported subnanometer gold nanoparticles (Au NPs/Cu²⁺-BNNS). Interestingly, our investigation reveals that Cu²⁺-BNNS exhibits strong peroxidase mimetic nanoenzyme activity, while Au NPs/Cu²⁺-BNNS exhibits excellent oxidase-like activity, that is, it can catalyze the oxidation reaction of the substrate in the absence of an oxidant such as H₂O₂. For example, Au NPs/Cu²⁺-BNNS can efficiently and selectively oxidize 3,3',5,5'-tetramethylbenzidine (TMB) and 3,3'-dimethylbiphenyl-4,4'-diamine (OT) coloration without the presence of horseradish peroxidase (HRP) and H₂O₂. It is worthy to note that AuNPs/Cu²⁺-BNNS-induced TMB coloration only takes 4 min to reach the platform, while the conventional HRP-H₂O₂ system takes more than 30 min to reach the platform. Further mechanism study shows that the zeta potential, oxidation potential, and steric hindrance of the oxidative chromogenic substrate determine the selectivity of oxidation coloration, while the oxidase-like properties of Au NPs/Cu²⁺-BNNS are derived from reactive oxygen species generated by the adsorbed oxygen, and Cu²⁺ ion can synergistically promote the oxidation process. Compared with conventional biological enzymes, Au NPs/Cu²⁺-BNNS has the advantages of being HRP free and H₂O₂ free, having high efficiency, low cost, and good stability, and is successfully demonstrated for the detection of carcinoembryonic antigen (a universal cancer biomarker) and H₂S (the third gaseous signal molecule).

ReactELISA method for quantifying methylglyoxal levels in plasma and cell cultures

Methylglyoxal (MG) is a toxic glycolytic by-product associated with increased levels of inflammation and oxidative stress and has been linked to ageing-related diseases, such as diabetes and Alzheimer's disease. As MG is a highly reactive dicarbonyl compound, forming both reversible and irreversible adducts with a range of endogenous nucleophiles, measuring endogenous levels of MG are quite troublesome. Furthermore, as MG is a small metabolite it is not very immunogenic, excluding conventional ELISA for detection purposes, thus only more instrumentally demanding LC-MS/MS-based methods have demonstrated convincing quantitative data. In the present work we develop a novel bifunctional MG capture probe as well as a high specificity monoclonal antibody to finally setup a robust reaction-based ELISA (ReactELISA) method for detecting the highly reactive and low-level (nM) metabolite MG in human biological specimens. The assay is tested and validated against the current golden standard LC-MS/MS method in human blood plasma and cell-culture media. Furthermore, we demonstrate the assays ability to measure small perturbations of MG levels in growth media caused by a small molecule drug buthionine sulfoximine (BSO) of current clinical relevance. Finally, the assay is converted into a homogenous (no-wash) AlphaLISA version (ReactAlphaLISA), which offers the potential for operationally simple screening of further small molecules capable of perturbing cellular MG. Such compounds could be of relevance as probes to gain insight into MG metabolism as well as drug-leads to alleviate ageing-related diseases.

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MG is challenging to quantify, here we present a simple and specific ReactELISA based approach and validate against LC-MS/MS.

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Sensitivity at low (nM) endogenous concentration in both human blood plasma and cell culture media.

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Impact of BSO treatment of HEK293 cells can be profiled in culture media.

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Potential use in cell-based phenotypic screen for small molecules modulating MG metabolism.

Aromatic secondary amine-functionalized fluorescent NO probes: improved detection sensitivity for NO and potential applications in cancer immunotherapy studies

Tumor-associated macrophages (TAMs), constituting up to 50% of the solid tumor mass and commonly having a pro-tumoral M2 phenotype, are closely associated with decreased survival in patients. Based on the highly dynamic properties of macrophages, in recent years the repolarization of TAMs from pro-tumoral M2 phenotype to anti-tumoral M1 phenotype by various strategies has emerged as a promising cancer immunotherapy approach for improving cancer therapy. Herein, we present an aromatic secondary amine-functionalized Bodipy dye 1 and its mitochondria-targetable derivative Mito1 as fluorescent NO probes for discriminating M1 macrophages from M2 macrophages in terms of their difference in inducible NO synthase (iNOS) levels. The two probes possess the unique ability to simultaneously respond to two secondary oxides of NO, i.e., N2O3 and ONOO-, thus being more sensitive and reliable for reflecting intracellular NO than most of the existing fluorescent NO probes that usually respond to N2O3 only. With 1 as a representative, the discrimination between M1 and M2 macrophages, evaluation of the repolarization of TAMs from pro-tumoral M2 phenotype to anti-tumoral M1 phenotype, and visualization of NO communication during the immune-mediated phagocytosis of cancer cells by M1 macrophages have been realized. These results indicate that our probes should hold great potential for imaging applications in cancer immunotherapy studies and relevant anti-cancer drug screening.

Visualization of methylglyoxal in living cells and diabetic mice model with a 1,8-naphthalimide-based two-photon fluorescent probe

Methylglyoxal (MGO), a dicarbonyl metabolite, is the most studied precursor of advanced glycation end-products (AGEs) and its elevated levels have also been associated with various pathologies. Hence, the development of effective methods for monitoring MGO in live cells and in vivo is of great importance for ascertaining the onset and progress of related diseases. Herein, we designed and synthesized an endoplasmic reticulum-targeting two-photon fluorescent probe called NI-OPD for the detection of MGO with high selectivity, sensitivity, and hypotoxicity. The probe was successfully applied for monitoring MGO in living cells and a diabetic mice model. The two-photon fluorescence images confirmed that the endogenous MGO in the liver and kidney tissues of diabetic mice is higher than that of normal mice. Furthermore, it revealed that after treatment with metformin, a widely used hypoglycemia drug, the diabetic mice showed a decreased concentration of MGO in liver and kidney tissues. Thus, NI-OPD may serve as a useful tool for the detection of MGO and for studying the relationships between MGO and pathological and biological processes in biosystems.

A rhodamine-based fast and selective fluorescent probe for monitoring exogenous and endogenous nitric oxide in live cells

A sensitive and selective fluorescent probe for fast detection of nitric oxide was synthesized by grafting a NO-trapper o-phenylenediamine onto a rhodamine fluorophore.

Selective and sensitive visualization of endogenous nitric oxide in living cells and animals by a Si-rhodamine deoxylactam-based near-infrared fluorescent probe

A Si-rhodamine deoxylactam-based near-infrared fluorescent probe has been successfully developed for the imaging of endogenous NO in living cells and mouse models.

Nitric oxide (NO) is a fundamental signaling molecule that regulates virtually every critical cellular function, and it is also a potent mediator of cellular damage in a wide range of conditions mainly via its secondary metabolite peroxynitrite (ONOO^–). In this work, we present an o-phenylenediamine (OPD)-locked Si-rhodamine deoxylactam, i.e.deOxy-DALSiR, as a near-infrared fluorescent probe for the selective and sensitive detection of NO in living cells and bodies. Not only could the probe overcome the limitations suffered by widely used and commercialized OPD-type fluorescent NO probes, such as the possible interferences by dehydroascorbic acid/ascorbic acid/methylglyoxal (DHA/AA/MGO), pH-sensitive fluorescence output, and short excitation and emission wavelengths, but it can also avoid serious interference from cysteine (Cys) found in the rhodamine lactam-based fluorescent NO probes developed later. What’s more, the probe is fairly sensitive for NO, as evidenced by its rapid fluorescence response rate (within seconds), huge fluorescence off–on ratio (6300-fold), and ultra-low detection limit (0.12 nM). Its effectiveness and practicability have been demonstrated by the successful imaging of endogenous NO in RAW 264.7 macrophages, pancreatic β-cells, and endothelial EA.hy926 cells, as well as in inflamed and diabetic mouse models.

Aromatic primary monoamine-based fast-response and highly specific fluorescent probes for imaging the biological signaling molecule nitric oxide in living cells and organisms

Two fast-response and highly specific NO fluorescent probes were developed, based on the reductive deamination reaction of p-methoxyaniline with NO in aerobic conditions.

An Approach for the Selective Detection of Nitric Oxide in Biological Systems: An in vitro and in vivo Perspective

A naphthalimide-based fluorescent probe, LyNP-NO, was designed and synthesized for the selective detection of exogenously and endogenously generated nitric oxide (NO) in C6 glial cells. In addition, LyNP-NO was also explored for monitoring endogenous NO levels in rat hippocampus at various tissue depths by stimulating the brain with N-methyl-d-aspartate (NMDA).

Nanoparticle-Based and Bioengineered Probes and Sensors to Detect Physiological and Pathological Biomarkers in Neural Cells

Nanotechnology, a rapidly evolving field, provides simple and practical tools to investigate the nervous system in health and disease. Among these tools are nanoparticle-based probes and sensors that detect biochemical and physiological properties of neurons and glia, and generate signals proportionate to physical, chemical, and/or electrical changes in these cells. In this context, quantum dots (QDs), carbon-based structures (C-dots, grapheme, and nanodiamonds) and gold nanoparticles are the most commonly used nanostructures. They can detect and measure enzymatic activities of proteases (metalloproteinases, caspases), ions, metabolites, and other biomolecules under physiological or pathological conditions in neural cells. Here, we provide some examples of nanoparticle-based and genetically engineered probes and sensors that are used to reveal changes in protease activities and calcium ion concentrations. Although significant progress in developing these tools has been made for probing neural cells, several challenges remain. We review many common hurdles in sensor development, while highlighting certain advances. In the end, we propose some future directions and ideas for developing practical tools for neural cell investigations, based on the maxim "Measure what is measurable, and make measurable what is not so" (Galileo Galilei).